How do you spot a staged interview before the footage tells you?

Reading about video shops casting actors to read AI-written political scripts, and it's got me thinking about all the interviews I've cut where something felt slightly off but I couldn't name it at first. For the editors and shooters here: what's the tell — eye movement, phrasing, the pause before they answer? I want to know if there's a reliable signal or if it's just instinct.